There are known catalyst components for the polymerization of olefins which are usable in the stereoregular polymerization of alpha-olefins and which consist of the product of the reaction of a halogenated Ti compound and of an electron-donor compound with an anhydrous Mg halide.
Said catalytic components are more particularly obtained by processes in which the anhydrous Mg halide is ground in the presence of the electron-donor compound and, optionally, in the presence of the Ti compound, and the ground product is subsequently made to react with a halogenated Ti compound, liquid under the reaction conditions, Examples of such catalytic components are described in Belgian Pat. No. 848,527.